[mrtg] Re: 95th percentile?

David C Prall dcp at dcptech.com
Fri Sep 24 19:17:19 MEST 1999

> Most folks looking for 95th percentile want to be able to calculate
> 95th percentile of all of the data over a given time period (usually a
> month).  MRTG only keeps its five minutes numbers for about two days,
> then it only stores averaged averages.  It's impossible to recreate
> true 95th percentile five minute average using reaveraged numbers; the
> peaks merely show the highest five minute peak across a two hour
> There's no way to determine how many five minute samples were that
> Some people have written scripts that archive a day's worth of
> samples each day, and then crank through that unaveraged data at the
> of the month.  The few folks I've talked to about this usually wrote
it on
> company time, and weren't permitted to release their script.  It's
> actually not that hard; the challenge is making sure that it scales
> (or can be reengineered to scale).
Thanks for the excellent example. So I went back and took a look at
above.net which supposedly had the 95th Percentile patched and found it
actually listed on the Monthly graph, along with a Red Line across at
this value. http://stats.sjc.above.net/traffic/

So what I am to understand is that they take this number and charge a
higher rate for all traffic above and beyond this value? So if I decide
to copy the entire Windows NT i386 directory over the wire to another
server at night, I am going to get charged an additional amount for this
half-hour burst of abnormal traffic? Since it wasn't critical it would
probably be cheaper to send the CD and have the local admin insert it
into the CD-ROM drive instead?

I don't really understand this, all that well. I've never had to
provision major connections beyond a T-1 to an ISP that was X amount a
month. No funny stuff in the contract that I saw.

David C Prall, MCNE MCSE          DCP Technologies
dcp at dcptech.com                       http://www.dcptech.com
dcppage at dcptech.com

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